A variety of tetracyclic quinolone compounds have been suggested to function by interacting with quadruplex-forming regions of nucleic acids and modulating ribosomal RNA transcription. See, for example, U.S. Pat. Nos. 7,928,100 and 8,853,234. Specifically, the tetracyclic quinolone compounds can stabilize the DNA G-quadruplexes (G4s) in cancer cells and thereby induce synthetic lethality in cancer cells. Since treatment of cells with G4-stabilizing agents can lead to the formation of DNA double strand breaks (DSBs), DSB formation induced by G4-stabilizing ligand/agent (such as the tetracyclic quinolones) treatment would be more pronounced in cells genetically deficient in, or chemically inhibited in, repair pathways including both non-homologous end joining (NHEJ) and homologous recombination repair (HRR). Furthermore, the tetracyclic quinolone compounds selectively inhibit rRNA synthesis by Pol I in the nucleolus, but do not inhibit mRNA synthesis by RNA Polymerase II (Pol II) and do not inhibit DNA replication or protein synthesis. It is suggested that targeting RNA polymerase I (Pol I) to activate p53 through the nucleolar stress pathway may results in selective activation of p53 in tumor cells. The p53 protein normally functions as a tumor suppressor by causing cancer cells to self-destruct. Activating p53 to kill cancer cells is a well validated anticancer strategy and many approaches are being employed to exploit this pathway. Selective activation of p53 in tumor cells would be an attractive method of treating, controlling, ameliorating tumor cells while not affecting normal healthy cells. The aforementioned tetracyclic quinolones are disclosed in U.S. Pat. Nos. 7,928,100 and 8,853,234, and the contents of this publication are herein incorporated by reference in their entirety for all intended purposes.
Those skilled in the pharmaceutical arts understand that crystallization of an active pharmaceutical ingredient offers the best method for controlling important physiochemical qualities, such as stability, solubility, bioavailability, particle size, bulk density, flow properties, polymorphic content, and other properties. Thus, there is a need for crystalline forms of the tetracyclic quinolones and processes to produce such forms. These crystalline forms should be suitable for pharmaceutical use.